Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
In order to supply power to the power grid, wind turbines need to conform to certain requirements. For example, wind turbines may need to offer fault ride through (e.g. low voltage ride through, zero voltage ride through) capability, which requires a wind turbine to stay connected to the power grid during one or more grid events corresponding to a change in the magnitude of grid voltage for a time duration. For example, when a grid event occurs, voltage in the system can decrease by a significant amount for a short duration (e.g. typically less than 500 milliseconds).
In the past, during such grid events, it has been acceptable for a wind turbine to be immediately disconnected whenever the voltage reduction occurs. However, as wind turbines continue to increase in size and penetration of wind turbines on the grid increases, it is desirable for the wind turbines to remain on line and ride through such disturbances.
Conventional wind turbine systems may include one or more power converters configured to convert an alternating current power to a direct current power, or vice-versa. Such power converters may include semiconductor devices such as IGBTs or MOSFETs that can be used as electronic switching elements for a variety of applications. For instance, IGBTs can be used in bridge circuits of a power converter. Often a freewheeling diode is coupled in parallel with the IGBT to control current flow in, for instance, a bridge circuit.
IGBTs typically include three terminals, including a gate, a collector, and an emitter. The IGBT can be operated as a switching element by controlling the gate-emitter voltage using a gate drive circuit. For instance, when the gate-emitter voltage exceeds a threshold voltage for the IGBT, the IGBT can be turned on such that current can flow through the collector and emitter of the IGBT. When the gate-emitter voltage is less than the threshold voltage for the IGBT, the IGBT can be turned off such that current flow through the collector and emitter is limited.